Crankshaft upper bearing question '94 90 Yam

[waterbill]

My flywheel is pretty tight when I try to move it side to side, but there is a slight--slight sense of a minute amount of side to side play(almost undetectable). Is there a good test to detect the allowable runout (.002in, per manual specs for the crankshaft)without disassembling the powerhead?

 

[bigbrownbuku]

Re: Crankshaft upper bearing question '94 90 Yam

play and runout are 2 different things. runout refers to shaft deviation rotating on an axis, ie if your shaft is bent it will have runout. a worn bearing will give you side play. if your engine runs and doesnt make any strange noises dont worry about bearing wear thats quite possibly normal.

 

[waterbill]

Re: Crankshaft upper bearing question '94 90 Yam

Thanks for the info on the definition of runout, BenC; the play is almost not there at all, but there has been some wear over the years(hours) I guess. I remember wanting to buy this boat with a Johnson 4Cyl.. I did a side play test on it, and it was really bad, so I ducked out. I have one more question: If this play gets worse, would it be wiser to just get a rebuilt powerhead for this older engine, or attempt to do a powerhead rebuild?

 

[rodbolt]

Re: Crankshaft upper bearing question '94 90 Yam

its very rare to see the upper bearing wear. it just goes round and round. there is no spec on lateral motion. however if there is any noticable up and down play odds are the bottom bearing is bad. yes some jonnyrudes have a considerable amount of lateral play but I havent seen an upper bearing failure just due to play. usually its a lubrication issue. I have seen some v6 yams with .01 or so lateral play that work fine. some jonnyrudes you can hear the upper bearing rattle for many years. the bottom bearing takes the radial and axial load. the upper just radial and just goes round and round.

 

[waterbill]

Re: Crankshaft upper bearing question '94 90 Yam

Thank you for the advice. I see what you mean. No up and down play at this time, so I'll rest easier, hoping to avoid a big water-bill.